The present invention relates to a method of forming a metallic film and a method of producing a semiconductor system, and particularly to a method of forming a metallic film and a method of producing a semiconductor system which are characterized by characteristic features in a heat treatment method.
Attendant on miniaturization of semiconductor systems, a groove wiring technology has come to be put to practical use. The groove wiring technology is a technology in which copper or a copper alloy is buried as a metallic wiring material in wiring grooves or both wiring grooves and connection holes formed in an insulating film, and thereafter excess portions of the metallic wiring material on the insulating film are removed by chemical mechanical polishing, whereby a groove wiring and/or plugs are formed of the metallic wiring material buried in the wiring grooves or in both the wiring grooves and the connection holes.
However, there has been the problem of deformation of the materials due to the differences between the wiring metal and the insulating film in the surroundings thereof in coefficient of thermal expansion, hardness and the like. In addition, there is also the problem that when the wiring metal itself is heat treated after being processed to a desired shape, thermal expansion and compressive forces from the surroundings cause distortion of crystals or changes in crystal structure, so that voids are generated in the wiring after cooling. These defects in shape degrade initial characteristics and reliability of operation on a long-term basis, such as defects in conduction of the wiring material. Each of copper and the copper alloy constituting the wiring material is formed into a film at a low temperature in order to prevent coagulation in a thin film condition in a sputtering method, and is restricted by the temperature of a plating solution tank in a plating method; in any case, the film of the wiring material is formed at a lower temperature as compared with the subsequent heat treatment. Therefore, the above-mentioned problems are conspicuous.
An example of variation of stress in a metal (for example, copper) surrounded by a material other than metal (for example, an oxide film, an organic insulating film, etc.) due to heating and cooling will be described referring to FIG. 8.
As shown in FIG. 8, the metal formed without heat treatment has a tensile stress at room temperature (for example, 23xc2x0 C.) (the condition of A), and upon being heated, the metal comes to have a compressive stress due to thermal expansion, but the metal gradually releases the compressive stress by crystal growth to come to a substantially stress-free condition (the process of transition from B to C). This is called a yield phenomenon. When being cooled, on the contrary, the metal returns to room temperature while relaxing the tensile stress (the condition of D), but the stress at this time is different from that in the initial condition (the condition of A). When the metal is heated for the second time and later, the metal shows a hysteresis change along the same loop as D-B-C-D.
At the time of heating and expansion while a compressive stress is being exerted on the metal in the route B-C, deformations occur in the inside of the metal and the material in contact therewith, which constitutes the above-mentioned problems in heat treatment.
On the other hand, in a production process of a semiconductor system, as shown in FIG. 9, a recessed portion 112 such as a wiring groove or both a wiring groove and connection holes, etc. is processed in a hard material film 111 such as silicon oxide (SiO2), silicon oxyfluoride (SiOF), etc., and then a metallic film 113 for filling up the recessed portion 112 is formed by such technology as sputtering, electrolytic plating, etc. When a heat treatment is conducted thereafter, the metallic film shows thermal expansion and crystal growth while moving upwards, and upon cooling, the tensile stress cannot be resisted, resulting in that voids 114 are generated at a lower portion and side portions of the metallic film 113.
In addition, as shown in FIG. 10, in a wiring structure in which an organic low dielectric constant film 211 formed on a substrate 210 is used as an inter-layer insulating film, the upper portion of a metallic wiring 212 formed in the organic low dielectric constant film 211 is covered with a protective film 213, for example, silicon nitride, silicon carbide or the like for preventing oxidation of the metallic wiring 212. There are some cases where such a structure is subjected to a heat treatment.
The organic low dielectric constant film 211 is subjected to a curing heat treatment after the film is formed by a coating system, for example. However, in the process of forming a structure composed of two or more layers, the first layer is reheated at the time of the curing heat treatment of the second layer. At the curing heat treatment temperature, the organic low dielectric constant film 211 is much lowered in hardness, so that it is easily deformed by thermal expansion of the metallic wiring 212 in contact therewith. Upon the subsequent cooling, the metallic wiring 212 shows a contraction, resulting in that voids 221 are generated between the metallic wiring 212 and the organic low dielectric constant film 211.
The present invention resides in a method of forming a metallic film and a method of producing a semiconductor system invented in order to solve the above-mentioned problems.
The method of forming a metallic film according to the present invention comprises the steps of: heating a metallic film to a temperature of the stress yield point of the metal xc2x150xc2x0 C. and holding the metallic film at the temperature for a predetermined period of time, and heating the metallic film to a temperature which is not lower than the holding temperature and at which growth of crystal grain diameter of the metallic film occurs, to thereby cause growth of crystal grain diameter of the metallic film.
According to the method of forming a metallic film, since the method comprises the step of heating the metallic film to a temperature of the stress yield point of the metal xc2x150xc2x0 C. and holding the metallic film at the temperature for a predetermined period of time, stress yield of the metallic film is completed in a temperature range in which thermal expansion amount is small. Since the method comprises the subsequent step of heating the metallic film to a temperature which is not lower than the holding temperature of the stress yield point of the metal xc2x150xc2x0 C. and at which growth of crystal grain diameter of the metallic film occurs, to thereby cause growth of crystal grain diameter of the metallic film, a heat treatment at a high temperature is conducted under the condition where the crystal of the metallic film is stable.
A first method of producing a semiconductor system according to the present invention comprises the steps of: forming a metallic film to be used for wiring on an insulating film provided with a recessed portion so as to fill up the recessed portion, heating the metallic film to a temperature of the stress yield point of the metal xc2x150xc2x0 C. and holding the metallic film at the temperature for a predetermined period of time, and heating the metallic film to a temperature which is not lower than the holding temperature and at which growth of crystal grain diameter of the metallic film occurs, to thereby cause growth of crystal grain diameter of the metallic film.
According to the first method of producing a semiconductor system, since the method comprises the step of heating the metallic film at a temperature of the stress yield point of the metal xc2x150xc2x0 C. and holding the metallic film at the temperature for a predetermined period of time, stress yield of the metallic film is completed in a temperature range in which thermal expansion amount is small. Since the method comprises, thereafter, the step of heating the metallic film to a temperature which is not lower than the temperature of the stress yield point of the metal xc2x150xc2x0 C. and at which growth of crystal grain diameter of the metallic film occurs, to thereby cause growth of crystal grain diameter of the metallic film, a heat treatment at a high temperature is conducted under the condition where the crystal of the metallic film is stable. Therefore, the generation of voids in the recessed portion upon cooling of the metallic film is suppressed, so that breakage of wiring and the like defects are prevented where the metallic film in the recessed portion is utilized as a wiring or a plug.
A second method of producing a semiconductor system according to the present invention resides in a method of producing a semiconductor system, comprising a step of heat treating a structural body comprising a first material portion which is softened when being heated and a second material portion comprised of a metal based material and formed in contact with the first material portion, wherein the heat treatment is conducted by heating to a temperature lower than the softening point of the first material portion to cause crystal growth of the second material portion with stress yield.
According to the second method of producing a semiconductor system, since the heat treatment by heating to a temperature lower than the softening point of the first material portion to cause crystal growth of the second material portion with stress yield is conducted, deformation of the first material is prevented.